Study On Extraction And Separation Of Vanadium And Molybdenum By Non-ionic Surfactant-sulfate Aqueous Two-phase Systems

The extraction and separation performance,extraction mechanism and thermodynamics of vanadium?V?and molybdenum?VI?were studied by aqueous two-phase systems consisting of non-ionic surfactants and sulfate,which is supposed to provide the basis theory to guide the actual production and scientific research in the future.Firstly,the co-extraction and stripping separation performances of V and Mo were carried out by aqueous two-phase systems consisting of sulfate and non-ionic surfactants,such as polyethylene glycol?PEG1000,PEG2000,PEG4000?,polyoxyethylene polyoxypropylene polyoxyethylene block copolymer?F68,L35?under weak acid condition.The effects of aqueous pH,T,concentration of surfactant,sulfate,vanadium and molybdenum on co-extraction of both mentals were investigated.The results indicated that the aqueous pH was the key factor affecting the co-extraction and the best pH was 2.0.The effect of the concentration of surfactants,sulfate,V and Mo on co-extraction was slight.With increasing T,the co-extraction rate of both metals decreased.The stripping separation performance of both metals was studied by aqueous two-phase system consisting of?NH₄?₂SO₄ aqueous solution and surfactant loaded with Mo and V.The effect of aqueous pH,concentration of?NH₄?₂SO₄,T and phase ratio on stripping performances was researched;The experimental results showed that the best aqueous pH was 10.0.With increasing concentration of?NH₄?₂SO₄,the stripping of V and Mo increased;T had a little effect on the stripping and precipitation rate of V,but had obvious effect on the stripping of Mo.With the increase of the phase ratio from 1.0 to 4.0,the stripping of Mo decreased significantly,while the stripping and precipitation rate of V basically unchanged.The results about the separation performance of V and Mo from waste catalyst under optimal conditions showed that the separation effect was pretty and the product's purity accorded with the national standard.The results on the cyclic performance of the used surfactant showed that the extraction and separation performance of both metals was no significant reduction after five cycles.Secondly,the separation performance of V and Mo was studied by aqueous two-phase systems consisting of sulfate and surfactants,such as PEG2000,L35 and octaphenyl polyoxyethyiene?Triton X-100?,under the high acid condition.The effect of aqueous pH,concentration of surfactant,V and Mo and temperature on the separation of V and Mo was experimented.The results indicated that the high separation factor can be obtained when the pH was 0.70?0.75 for the aqueous two-phase system consisting of L35 and sulfate.With increasing T,the extraction rate of V decreased,while the extraction rate of Mo increased,and the separation factor of both metals increased.Compared with V concentration,the concentration of Mo had greater effect on the separation of both metals.Under the optimal extraction conditions,the extraction rate of Mo reached more than 90%,while the extraction rate of V was less than 20%,and the separation factor of both metals reached 47.Finally,the extraction mechanism of both metals was studied by the phase equilibrium of V?V?-Mo?VI?-H₂O system,infrared spectrum,Raman spectrum and dynamic light scattering.The results revealed that the heteropolyacid anions of both metals and homopolyacid anions of Mo were extracted into the surfactant-rich phase by electrostatic attraction between pseudo-cations formed by the protonation of oxyethylene units in surfactant molecules and heteropolyacid or homopolyacid anions.The van't Hoff nonlinear equation was adopted to study the thermodynamic parameters of the phase transfer of homo?hetero?polyacid anions from salt-rich phase to surfactant-rich phase.The results showed that the phase transferring of the solutes conformed to nonlinear van't Hoff equation.The transferring free energy of the heteropolyacid and homopolyacid anions was all negative,indicating that the phase transfer process of both anions was spontaneous.The enthalpy and entropy change of the heteropolyacid anions were negative,indicating that the transferring driving force was enthalpy.The enthalpy and the entropy change of homopolyacid anions were positive,indicating that the transfeering driving force was driven by entropy.